Merge pull request #4 from kriomant/master

Move `map` method from `FieldPf` to `Field` [issue #3]
next version will be 2.1.0

B/c we are "adding few functionality in backwards-compatible manner" http://semver.org/
Apply field conversion to arrays
Merge pull request #5 from kriomant/apply-field-to-arrays

Bug fix & improvement: Optimal array field conversion